I'm half writing this down to organize my thoughts, and half in the hopes that someone might see something. I've been working on this for a few months now, and it is intermittent, and it likes to mess with me by going away after I replace a part for a day so I think its fixed :P

I think the fuel trims may be high but this was within 1 minute of starting cold.

Main Symptoms:
Cold rough Idle - it Idles rough for 1-2 mins when starting cold, usually misfires
When its wet, its worse (it seems)
14 mpg max

Other stuff I've noticed:
Intermittent fuel smell in and around the car
Intermittent vibration at idle

Codes
p0306 # 6 misfire
p0326 Knock sensor out of range I think

Freeze Frame:
FUELSYS1: CL
FUELSYS2: ---
LOAD_PCT (%): 37.2
ETC(): 19 (Coolant temp, Celsius)
SHRTFT1 (%): 97.6
SHRTFT2 (%): 138.2
LONGFT1 (%): 100.0
LONGFT3 (%): 150.0
SHRTFT2 (%): 111.7
SHRTFT4 (%): 197.6
LONGFT2 (%): 101.5
LONGFT4 (%): 189.8
RPM (/min): 1208
VSS(km/h): 0

Things that are new (most were not replaced due to this issue)
- all plugs
- all wires
- coil
- tps
- idle air control valve
- DPFE on the manifold
- Fuel Cap

Things that were cleaned:
MAF (The right spray)
Throttle body (The right spray)

What I am doing next:
- Compression test
- Check the knock sensor wiring

 

So we passed the cylinder compression test - they were all at 150 exactly. Engine was warm.

And, the last two days the misfire on cold start has been gone, even though its been pretty cold this past few days (and wet).

It's like I did something just by pulling the plugs - maybe a wire was loose?

Anyway this has a habit of coming back so we'll see ...

 

Well it came back. Its crazy and I don't know what to do.

@RonD

What do you think? Compression test passed, but it got better after the compression test, for a day or two.

Does holding the gas pedal down while starting (for the comp test) also reset anything in the computer?

It's the exact same issue too, misfire on #6 - goes away and runs like a champ when it gets to about 100 engine coolant temp (F)

We tell ppl here to always do a compression test when you have a misfire, but what do you do if compression passes?

Is it fuel injector time? EGR? Vaccume?

Gah this is annoying lol

Thanks

 

So update on this one, I am really lost now.

I was still getting the misfire in that 2 minutes as it first warmed up in the morning. It was always on cylinder 6. Since I have replaced plugs, wires, coil pack, I've ruled out spark. I've done a compression check and it's fine.

So my thinking was, a leaky injector in #6 leaking fuel into the cylinder over night as the engine sits, and then taking a bit to burn / blow that out in the morning (which is when the misfire code usually comes).

So I replaced all 6 injectors.

This morning, still the exact same problem.

What could be causing a cylinder specific misfire, only at cool temps, (first 1-2 mins of running in the morning) ?

What is happening in those first 2 minutes fuel wise?

Thanks!

 

I've been reading on this post, which is similar: https://www.ranger-forums.com/2-9l-3...art-up-154733/

Which prompted me to go back and look at my numbers, and something I missed earlier, why am I in CL (closed loop) at 19 degrees C ? The engine coolant sensor has been replaced (the one next to the thermostat, with 2 wires).

Maybe a stuck open thermostat letting too hot coolant to the sensor too early and trying to run off the o2 sensor data before it's hot enough?

 

Is the 19 ℃ engine temp. or outside temp? I'd expect the engine to be in CL at that temperature.

When were (if ever) the oxygen sensors replaced? I recall a test station that replaced everything but the oxygen sensors (93 Ranger 3.0). It passed smog but barely.
Then I had the oxygen sensors replaced (I had no record of such maintenance) and the idling and smog test scores improved vastly.

I don't know if holding down the gas pedal resets anything in the computer. That's done when you think the engine is flooded.

 

Th 19 is engine coolant temp.

I have no idea on the O2 sensors.

Probably should look at those as well.